In the manufacture of pneumatic tires, elastomeric components, some of which are reinforced by cords of textile or wire, are formed as long strips. These strips are assembled together to form a carcass subassembly in a first stage of assembly. This carcass typically has one or more cord reinforced plies, a pair of bead cores and an air impervious liner. Additional strips of material such as apexes, shoulder gum strips, chippers, and chaffers may also be included in this first stage of tire assembly.
In a second stage, the tread rubber and belt or breaker reinforcing structure is typically applied to the carcass after the carcass has been toroidally shaped on the tire building drum. The tread rubber may be of one or more homogeneous compounds. Typically, the tread is a sophisticated composite of many different rubber materials co-extruded to form a tread strip. The belt or breaker reinforcing layers generally include two layers or more of cross plies reinforced by equal, but oppositely oriented, cords of textiles, such as nylon or aramid, or wire, such as steel. Additionally, overlays or underlays of generally circumferentially oriented cords may be added as additional layers.
Tires typically have been built using this two-stage assembly. Once assembled, this uncured assembly of the components may be placed in a curing mold to be vulcanized to form a finished tire. High speed and efficient ways to manufacture tires require the processes to be reliable and fast. Accordingly, manufacturers of tires have experimented and perfected many ways to improve on the basic two-stage assembly of tires.
An expansible and contractible transfer ring may convey a breaker/tread assembly from a tire building drum in a tire building machine to a tire carcass mounted on a tire shaping machine. A separate tread/breaker building drum may vary in size to accommodate different sizes of tires.
Thus, the assembly of a tread/belt to a tire carcass may be accomplished off-line, or separate from, the carcass building machine. Once formed into a ring, these tread/breaker assemblies may be moved to encircle a tire carcass, the carcass may be inflated to contact the inner surface of the tread/breaker assembly and stitched together by a roller mechanism to form a green, or uncured, tire assembly to be placed into a curing mold.
Conventional tire molds, whether two piece molds or segmented molds, form the tread surfaces by pressing groove forming ribs and sipe forming blades into the tread rubber as the tire is cured. As this is done, the belt cords, particularly those directly under the groove-forming ribs, may deflect in small, but noticeable, undulations. These undulations may create a variety of changes across the tread that actually may alter the surface or change the amount of tread rubber across the otherwise normal appearing tire. These non-uniformities may lead to mass imbalance issues, irregular wear, and a variety of associated ride/handling/noise performance issues. A goal in tire manufacturing is to minimize unpredictable non-uniformities in manufacturing while also building the tire in a very cost-efficient manner.